Here is how you can get a copy of the previous version of macOS on your Mac.
How to Get a Previous macOS Installer
Getting hold of a previous macOS installer is not easy as it seems. Apple doesn’t feature exclusive links to the previous versions. If you’re running a version of macOS prior to Mojave, you can download the installers by accessing the Purchased tab in the App Store. The Purchased tab shows all your Purchases / Downloads from the App Store, allowing you to download the previous installers from there. This method will only work if you’ve previously downloaded the installers from the App store. If you have another Mac or know a friend who has one running a previous version of macOS (prior to Mojave), it’s advisable to use that system to log onto your Apple ID and download the installers. It’s an easier way than using the separate installers listed below. When Apple launched macOS Mojave, the App Store was redesigned, and Apple removed the previous versions of macOS from the Purchased tab. Thus, if you’re running macOS Mojave or later, you’ll need to use the direct links to the respective macOS versions on the Mac App Store to download the installers. These installers only work on a specific combination of hardware/software and may not work for you.
macOS Mojave
Downloading macOS Mojave is easy: simply access the Mojave page on the Mac App Store and click on “Get.” This will open Software Update and will start downloading the Mojave installer. Once dowloaded, make sure you copy the installer out of the Applications folder and make a copy in some other location, since the installer will be deleted once the installation is complete.
macOS High Sierra
You can download macOS High Sierra directly from the Mac App Store. Make sure to back up the installer before installing macOS High Sierra.
macOS Sierra
Apple removed macOS Sierra from users’ Purchased tab when they introduced macOS High Sierra, but it is still possible to download on Macs running High Sierra or earlier with this link.
Macs running macOS Mojave will see an “Update Not Found” error message when downloading this file.
OS X Mavericks, El Capitan, Yosemite, Mountain Lion and Lion
You can download these versions from the Purchased tab of Mac App Store if you’ve downloaded them once before. This should work on all Macs running Mac High Sierra or earlier. There’s no guarantee it’ll work on Macs running later versions. Some users have reported seeing the installers in the Purchased tab, but it didn’t work for me. If the method does indeed work, you’ll be able to separately download the installer onto your Mac and then install it on your system.
OS X Lion, Mountain Lion, Leopard or Earlier
Apple still sells a physical disc of OS X Snow Leopard that you can purchase. You will need a CD/DVD drive to install it on your Mac. Similarly, Apple also sells Mac OS X 10.7 Lion and Mac OS X 10.8 Mountain Lion on their website. Apple will send you a download code to use it on the Mac App Store, and since the Mac App Store was initially introduced with OS X Snow Leopard, you’ll need to be running it in order to install Lion or Mountain Lion. For earlier versions, try searching eBay for boxed versions of the installer since they’re not available as downloads.
Using the links mentioned above, you’ll be able to download previous installers of macOS, albeit with some difficulty. Never download the installer from a third-party source or a torrent website, since the installer may have been tampered with and could pose a security threat to your Mac.
